TITLE: Constness, containers, and iterators


[ This came in response to discussions about dealing with both
  const and non-const containers with iterators. In particular,
  handling both const and non-const containers seems to imply 
  having two iterator kinds. -adc ]


RESPONSE: michael@selway.umt.edu (Michael Babcock)

Is there a standard solution to this problem? Any hints will be greatly
appreciated. The only thing I can think of is to have two separate iterator
classes, the normal one and another one just for when I need to manipulate
the list being iterated.


RESPONSE: fjh@munta.cs.mu.OZ.AU (Fergus Henderson), 18 Sep 94

There are two standard solutions.  The first is the one you mention,
the second is to use index-style iterators rather than pointer-style
iterators.  Then you only need one iterator class, because you can
overload the `[]' operator on const.

	Collection c;
	// ...
	for (Iterator i = c.first(); c.valid(i); c.next(i)) {
		c[i] = 42;
		// calls `Collection::operator[](Iterator)'
	}

	const Collection const_c;
	// ...
	for (Iterator i = const_c.first(); const_c.valid(i); const_c.next(i)) {
		cout << const_c[i];
		// calls `Collection::operator[](Iterator) const'
	}